Conventionally, there are audio devices such as cassette tape recorders as apparatus for recording and playing back analog audio signals, and there are video tape recorders as apparatus for recording and playing back analog video signals.
There are some conventional analog audio devices, such as cassette tape recorders, which have an operation mode of dubbing an analog audio signal recorded on a magnetic tape at a double-speed of the tape speed at the normal playback. In these analog audio devices, the playback audio is also output at the double-speed dubbing, whereby monitoring of the dubbing state is made possible.
In the existing videotape recorder (VTR), a played-back analog video signal is output to the video output terminal in the playback state such that an analog video signal recorded on the magnetic tape is played back. Thus, the video output terminal of the first VTR is connected to the video input terminal of the second VTR, whereby the analog video signal is played back by the first VTR while the played-back analog video signal is recorded by the second VTR. That is, the dubbing of the analog video signal can be performed with monitoring the state of the dubbing.
However, this dubbing of the analog video signal using two VTRs is possible only at the normal playback speed and impossible at a higher speed than the normal playback speed. For example, the analog video signal can be played back at a higher speed on the playback end VTR, but the analog video signal cannot be recorded at a higher speed on the record end VTR.
Further, in recent years, record/playback apparatuses such as MD recorders for digital audio data or record/playback apparatuses such as DVD recorders for digital video data have been put to practical use.
In these record/playback apparatuses for the digital data, the digital data can be reproduced without the decline in the sound quality or image quality. Thus, itis considered that in these record/playback apparatuses, the storage or edition of image or sound information will be increasingly performed in the format of digital data.
Accordingly, record/playback apparatuses which are obtained by mounting a storage device for digital data such as a hard disk drive on the DVD recorders are also intended to be put to practical use.
FIG. 6 is a block diagram schematically illustrating a record/playback apparatus which is obtained by mounting a hard disk in the DVD recorder.
The record/playback apparatus 10 as shown in FIG. 6 has a hard disk 10a as a large-capacity data storage medium, an optical disk drive 10b for performing data access to an optical disk, an interface unit 10c for a display unit 20 outside the record/playback apparatus, and a signal processing unit 10d for performing digital data access to the hard disk 10a, the optical disk drive 10b and the interface unit 10c, as well as performing various processes for the digital data such as decoding.
In the hard disk 10a, various types of digital data are stored, and, for example, digital video data are coded and stored as a video stream. The signal processing unit 10d performs, as signal processing for digital data, the data transfer process for reading a video stream Sv from the hard disk 10a and supplying the video stream Sv to the optical disk drive 10b, and the decoding process for reading the video stream Sv from the hard disk 10a, decoding the read video stream, and outputting decoded data to the interface unit 10c and the like. The interface unit 10c converts the digital video data Dv obtained by the decoding of the video stream in the signal processing unit 10d into analog video data Av, and supplies the analog video data Av to the display unit 20.
Next, a case where the display and dubbing of digital video data is performed using the so-constructed record/playback apparatus will be briefly described.
When the display of the digital video data is to be performed by the record/playback apparatus 10, initially the video stream Sv is read from the hard disk 10a to the signal processing unit 10d. Then, the readout video stream Sv is decoded by the signal processing unit 10d, and digital video data Dv obtained by the decoding of the video stream Sv are output to the display unit 20 as the analog video data Av via the interface unit 10c. In this case, the average data transfer rate at which the video stream Sv is transferred from the hard disk 10a to the signal processing unit 10d is the normal transfer rate corresponding to the normal playback process in cases where the display of the digital video data is performed.
When the dubbing of the video stream Sv is performed, the video stream Sv is read from the hard disk 10a to the signal processing unit 10c, and the read video stream Sv is supplied to the optical disk drive 10b. Then, in the optical disk drive 10b, a process for writing the video stream Sv on an optical disk is carried out. In this case, the transfer rate of data (video stream) to be transferred from the hard disk 10a to the signal processing unit 10d, in other words, the transfer rate of data to be transferred from the hard disk 10a to the optical disk drive 10b corresponds to the data writing ability of the optical disk drive 10b and generally is a high-speed transfer rate, such as twice, four times or eight times as high as the normal transfer rate.
In the description of FIG. 6, the case where the video stream Sv is transferred from the hard disk 10a to the optical disk drive 10b is shown. However, when the video stream Sv is transferred from the hard disk 10a to another hard disk, the transfer rate of the video stream Sv is much higher than in the case where the video stream is transferred to the optical disk drive 10b. 
In the record/playback apparatus 10, the display of digital image data or dubbing of a video stream can be performed, but the display of digital image data while performing the dubbing of the data cannot be performed, whereby the state of the dubbing cannot be monitored.
This is for the following reasons. The decoding of coded digital video data (video stream) is performed at a data processing speed corresponding to the data transfer rate at the normal playback. On the other hand, when the dubbing of the video stream is performed, data access to record media such as a hard disk is performed at a higher speed than the data transfer rate at the normal playback. Therefore, the decoding process corresponding to the data transfer rate at the normal playback cannot be simply applied to data (video stream) at the time of dubbing, which are accessed at a higher data transfer rate than the data transfer rate at the normal playback.
For example, also when digital video data which have been coded in a variable rate coding process corresponding to the MPEG (Moving Picture Experts Group) standard, typified by data recorded on a DVD (Digital Video Disk), are dubbed, the dubbing of the digital video data is performed at a higher average transfer rate than the average transfer rate required for the normal playback. Therefore, also in this case, the decoding of the coded digital video data (video stream) cannot be performed in parallel with the dubbing of the data and thereby the state of the dubbing cannot be monitored.
The above-mentioned problem that the dubbing state cannot be monitored at the time of high-speed dubbing is not confined to the digital video data, but the similar problem occurs in the case of digital audio data. That is, also when the high-speed dubbing of coded digital audio data is performed, it is impossible to decode the data and monitor the audio accurately.